1. Field of the Invention
The present invention relates to a semiconductor element, typically, a thin film transistor (TFT), using particularly a crystalline semiconductor film as a semiconductor layer including a channel forming region, a source region, and a drain region. Also, the present invention relates to a semiconductor device using such a TFT as a driver circuit or a switching element of a pixel (particularly, a liquid crystal display device or a light emitting device) and a manufacturing technique thereof. Further, the present invention particularly relates to a semiconductor device having a structure in which a light shielding property is improved and a manufacturing technique thereof.
2. Description of the Related Art
In recent years, a liquid crystal projector in which characteristics such as miniaturization and weight reduction are improved has been used in various situations. In response to that, competition of development for providing a liquid crystal projector having a smaller size and lighter weight is intensified. The liquid crystal projector is constructed so as to project an image and the like displayed on a liquid crystal display device and the performance of the liquid crystal projector is greatly influenced by a display quality of the liquid crystal display device.
As to the liquid crystal display device, the mainstream is one in which liquid crystal is sealed between a substrate in which a TFT and a pixel electrode are formed (hereinafter referred to as a TFT substrate) and a substrate in which a counter electrode is formed (hereinafter referred to as a counter substrate) and an alignment of the liquid crystal is controlled by an electric field produced between the pixel electrode and the counter electrode to display an image.
In recent years, an active matrix type liquid crystal display device (liquid crystal panel) having several million pixels in a pixel portion is greatly used as a liquid crystal display device. In such a liquid crystal panel, a TFT is provided in each of pixels as a switching element for providing a potential to each of pixels and a pixel electrode is provided in each TFT. When the TFT is turned on, the potential of the pixel electrode is set. When the TFT is turned off, the potential of the pixel electrode is kept by charges stored in a storage capacitor element (hereinafter referred to as a storage capacitor).
When the potential of the pixel electrode is changed while the TFT is in an off state, a display quality is deteriorated. Thus, it is required for an active matrix type TFT substrate that a leak current of the TFT is suppressed, a sufficient storage capacitance is obtained for each of pixels, and the amount of charges stored in the storage capacitor is sufficiently larger than that lost by a leak current.
Also, in the case of a transmission type liquid crystal panel, in order to increase the intensity, it is necessary to increase an occupying ratio of an opening portion, that is, a region which is intended to control display in a pixel (for example, a region through which light is transmitted and which contributes to display in the case of a transmission type display device, a region from which light is reflected and which contributes to display in the case of a reflection type display device, a region in which an organic light emitting layer sandwiched by electrodes emits light and which contributes to display in the case of a display device using an organic light emitting element, or the like).
Incidentally, in the case where the above-mentioned liquid crystal panel (in particular, a transmission type liquid crystal panel) is used for a liquid crystal projector, when light is incident into the semiconductor layer of a TFT, since a leak current due to photo-excitation (hereinafter referred to as a photo leak current) is caused, it has an adverse affect on display. Thus, a light shielding layer is provided in the liquid crystal panel. For example, when a light source of the projector is located in a counter substrate side, the light shielding layer is formed between a pixel electrode and a TFT to block light from the light source, or the light shielding layer is formed between a substrate and a semiconductor layer to block light reflected from a projection lens or the like. Also, according to Japanese Patent Application Laid-Open No. 2000-164875, a concave portion is provided in a substrate and a lower light shielding film is formed on the entire inner wall surface of the concave portion. Thus, the channel forming region of a TFT is formed so as to be buried in the concave portion. Also, an upper light shielding film is formed together.
However, according to the structure disclosed in the above publication, unevenness is formed near a TFT on which various wirings are concentrated. Thus, a possibility of reducing a yield is high because, at the time of wiring formation, a short circuit and a break of wirings are easily caused, or the wirings are easily deteriorated by the concentration of an electric field.
Also, according to the structure disclosed in the above publication, a gap is present between the upper light shielding film and the lower light shielding film. Thus, in the case of such a structure, there is also a possibility that a photo leak current by stray light is caused. Further, since the concave portion is provided in the substrate, there is a possibility that the mechanical strength of the substrate is reduced.
In the case of a projector for which a high intensity and a high definition are required, first, the intensity of a lamp used as a light source is increased to increase a display brightness. Second, the number of pixels in a panel used for an optical system is increased to obtain a higher definition. However, in the conventional methods of forming the light shielding film between the pixel electrode and the TFT and of forming the light shielding film between the substrate and the semiconductor layer, there is a problem that light diffracted by end portions of the light shielding film is incident into the semiconductor layer to cause a photo leak current.
Further, with increasing the intensity of the light source, an adverse affect on the TFT by the diffracted cannot be neglected any longer.
Also, when a thin insulating film is used for isolating the light shielding film and the TFT, the intensity of the diffracted light in the position of the TFT can be reduced to a negligible extent. However, when the insulating film is made thinner, a parasitic capacitance produced between the TFT and the insulating film is increased. Therefore, a problem occurs in that an operation of the TFT is influenced by a potential of the light shielding film.
Also, when a width of the light shielding film is expanded, a problem that diffracted light is incident into the TFT can be solved. However, it is natural to reduce an aperture ratio. In addition, since the requirement for a high definition of display is satisfied by increasing the number of pixels, a size of respective pixels is decreased. Thus, a reduction in an aperture ratio due to the expansion of the width of the light shielding film and a reduction in brightness accompanied by such a reduction become a large problem.
Also, only when the width of the light shielding film is expanded, a problem that stray light produced by unintended scattering in an interlayer insulating film is incident into the TFT (in particular, the semiconductor layer) cannot be solved. With increasing the intensity of the light source as described above, the influence of the stray light also cannot be neglected.
Also, in a TFT including an active layer having a crystalline structure, which has been actively used because of its high field effect mobility and the like, a photo leak current tends to increase as compared with a TFT including an amorphous semiconductor layer. If the TFT have no sufficient storage capacitance, stored charges are decreased by the leak current to change the amount of light to be transmitted, which becomes a cause for reducing a contrast in image display. Thus, it is necessary to form a storage capacitor element capable of securing a sufficient capacitance in a liquid crystal panel.
However, when an area of the storage capacitor is expanded in two dimensions to secure the sufficient capacitance, an occupying ratio of the storage capacitor element to an area of a pixel is increased to reduce an aperture ratio.
Further, in order to improve a yield, it is necessary to use a structure in which a break of wiring and the like are not caused by unevenness due to the presence of the storage capacitor.
Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a method of realizing a semiconductor device having a structure in which a sufficient light shielding property is compatible with a sufficient storage capacitance without reducing an aperture ratio.
In order to solve the above problems, the present inventor considered a structure for reducing diffracted light and stray light, which are incident into the semiconductor layer of a TFT by forming a light shielding film so as to cover and fit the TFT.
FIG. 1A shows one example of a structure of a pixel for which the present invention is adopted.
A light shielding film is formed between a pixel electrode and a TFT. In this specification, a light shielding film in which at least a portion thereof is formed between the pixel electrode and the TFT is called an upper light shielding film. In the pixel, a groove is formed between a region through which light is transmitted and for which display is controlled and the TFT, and then a conductive film as the upper light shielding film is formed. It is different from a conventional structure having the light shielding film formed between the TFT and the pixel electrode. That is, the upper light shielding film is continuously formed from a region located between the pixel electrode and the TFT to a region through which light is transmitted so that the TFT is covered and fit with the upper shielding film.
FIG. 1B shows another structure of a TFT for which the present invention is adopted.
A TFT composed of a semiconductor layer, a gate insulating film, and a gate electrode is formed and an interlayer insulating film is formed. After that, the gate insulating film and the interlayer insulating film in a region through which light is transmitted and for which display is controlled in a later stage and its surrounding region are removed. In this specification, a hole-shaped region (having a wall surface and a bottom surface) is called a window for the sake of simplification, in which a portion of the gate insulating film and a portion of the interlayer insulating film are removed and which has the substantially same area as a region (opening portion) intended to control display in a display device. The upper light shielding film and the insulating film are formed in the wall surface of the window. Thus, although the area of the opening portion is smaller than that of the window by the film thickness, it can be said that the area of the window and that of the opening portion are substantially identical to each other.
Here, when the window shown in FIG. 1B is compared with the groove shown in FIG. 1A, since the window has a small aspect ratio, the formation of the upper light shielding film is simple and easy. Next, a light shielding film is continuously formed to cover a region from the top of the TFT to the side surface of the window. After that, the light shielding film formed on the bottom surface of the window (in particular, a region through which light is transmitted) is removed, and then an insulating film is formed and the window is filled with a transparent organic resin film made of acrylic or the like for leveling. Next, an insulating film is formed such that the light shielding film is not in contact with a pixel electrode and then the pixel electrode is formed. Thus, the structure is obtained such that the TFT is covered and fit with the upper light shielding film and the window is formed by removing the interlayer insulating film and filled with the transparent organic resin insulating film for leveling.
In the case of the above structure, an area of the region (window) in which a portion of the gate insulating film and a portion of the interlayer insulating film are removed is substantially equal to that of the region (opening portion) intended to control display in a pixel. In addition, the region (opening portion) intended to control display has a smaller area than that of the region (window) in which at least the portion of the gate insulating film and the portion of the interlayer insulating film are removed.
FIG. 1C shows another structure of a pixel for which the present invention is adopted. In the example shown in FIG. 1C, in order to also block light incident from a substrate side, a light shielding film is formed between the substrate and a semiconductor film before the formation of the semiconductor film. Note that the light shielding film formed between the substrate and the semiconductor film is hereinafter called a lower light shielding film in this specification. Next, a TFT composed of a semiconductor layer, a gate insulating film, and a gate electrode is formed and an interlayer insulating film is formed. After that, the gate insulating film and the interlayer insulating film which are formed in a region for which display is controlled later and its surrounding region are removed to form a window. Next, a light shielding film is continuously formed from the top of the TFT to the window. After that, the lower light shielding film formed on the bottom surface of the window and the upper light shielding film are removed to form an opening portion (region intended to control display). Next, an insulating film is formed and the window is filled with a transparent organic resin film made of acrylic or the like for leveling. Next, an insulating film is formed such that the light shielding film is not in contact with a pixel electrode and then the pixel electrode is formed. Thus, the structure is obtained such that the TFT is covered with the upper light shielding film and completely light-shielded by the upper light shielding film and the lower light shielding film. Note that, if a ground potential is provided for the upper light shielding film and the lower light shielding film, the TFT can be electrically shielded.
Further, when a color filter is formed in a counter substrate side, there is a problem that a matching accuracy between the counter substrate and a TFT substrate is reduced due to a decrease of a pixel size for high definition display. Thus, a method of forming the color filter in a TFT substrate side is considered. However, for the orientation of liquid crystal, it is necessary to form a pixel electrode after the formation of the color filter. Here, since the color filter having a thickness of 1 xcexcm or larger is required, it is difficult to electrically connect the pixel electrode and a drain electrode which are isolated by the color filter.
Therefore, in the examples shown in FIGS. 1B and 1C, when the window is filled with a photoresist film colored with R (red), G (green) or B (blue) for leveling, the same function is obtained as in the case of the color filter formed in a counter substrate.
Also, although not shown, in the structure shown in FIG. 1B or 1C, the upper light shielding film is made of a material having a high reflectance such as aluminum. In addition, the upper light shielding film on the bottom surface of the region (window) in which at least the portion of the gate insulating film and the portion of the interlayer insulating film are removed is not removed and is used as a reflective plate. In this case, a reflection type display device can be also obtained.
According to the present invention, there is provided a semiconductor device comprising: a substrate; a TFT located over the substrate; a pixel electrode electrically connected with the TFT; an upper light shielding film located between the TFT and the pixel electrode; at least one interlayer insulating film formed over the TFT; and a window formed between the pixel electrode and the substrate by removing the interlayer insulating film, the semiconductor device being characterized in that the upper light shielding film is continuously formed from a bottom surface of the window to a surface of the interlayer insulating film to cover and fit the TFT, and an area of the window is substantially equal to that of the opening portion.
Also, according to the present invention, there is provided a semiconductor device comprising: a substrate; a lower light shielding film located on the substrate; a TFT located over the lower light shielding film; a pixel electrode electrically connected with the TFT; an upper light shielding film located between the TFT and the pixel electrode; at least one interlayer insulating film formed over the TFT; and a window which is formed between the pixel electrode and the substrate by removing the interlayer insulating film and provided with an opening portion, the semiconductor device being characterized in that the upper light shielding film is continuously formed from a bottom surface of the window to a surface of the interlayer insulating film to cover and fit the TFT, and an area of the window is substantially equal to that of the opening portion.
Also, according to the present invention, there is provided a semiconductor device comprising: a substrate; a lower light shielding film located on the substrate; a TFT located over the lower light shielding film; a pixel electrode electrically connected with the TFT; an upper light shielding film located between the TFT and the pixel electrode; at least one interlayer insulating film formed over the TFT; and a window formed between the pixel electrode and the substrate by removing the interlayer insulating film, the semiconductor device being characterized in that the upper light shielding film is continuously formed from a bottom surface of the window to a surface of the interlayer insulating film to cover and fit the TFT, and the lower light shielding film is in contact with the upper light shielding film at the bottom surface of the window.
Also, according to the present invention, there is provided a semiconductor device comprising: a substrate; a lower light shielding film located on the substrate; a TFT located over the lower light shielding film; a storage capacitor element formed in parallel to the TFT; a pixel electrode electrically connected with the TFT; an upper light shielding film located between the TFT and the pixel electrode; at least one interlayer insulating film formed over the TFT and the storage capacitor element; and a window formed between the pixel electrode and the substrate by removing the interlayer insulating film, the semiconductor device being characterized in that the lower light shielding film is in contact with the upper light shielding film at a bottom surface of the window.
Also, according to the present invention, there is provided a semiconductor device comprising: a substrate; a TFT located over the substrate; a pixel electrode electrically connected with the TFT; a light shielding film located between the TFT and the pixel electrode; at least one interlayer insulating film formed over the TFT; and a window formed between the pixel electrode and the substrate by removing the interlayer insulating film, the semiconductor device being characterized in that the window is filled with a transparent organic insulating film for leveling, and the light shielding film is continuously formed from a bottom surface of the window to a surface of the interlayer insulating film to cover and fit the TFT.
Also, according to the present invention, there is provided a semiconductor device comprising: a substrate; a lower light shielding film located on the substrate: a TFT located over the lower light shielding film; a pixel electrode electrically connected with the TFT; a laminate body which is located between the TFT and the pixel electrode and provided with a plurality of upper light shielding films and a plurality of insulating films which are alternately laminated; at least one interlayer insulating film formed over the TFT; and a window formed between the pixel electrode and the substrate by removing the interlayer insulating film, the semiconductor device being characterized in that the window is filled with a transparent organic insulating film for leveling, and the plurality of laminated light shielding films are formed from a bottom surface of the window to cover and fit the TFT.
Also, according to the present invention, there is provided a semiconductor device comprising: a substrate; a lower light shielding film located over the substrate; a TFT located on the lower light shielding film; a pixel electrode electrically connected with the TFT; a laminate body which is located between the TFT and the pixel electrode and has a plurality of upper light shielding films and a plurality of insulating films which are alternately laminated; at least one interlayer insulating film formed over the TFT; and a window formed between the pixel electrode and the substrate by removing the interlayer insulating film, the semiconductor device being characterized in that the window is filled with a transparent organic insulating film for leveling, the plurality of laminated light shielding films are formed from a bottom surface of the window to cover and fit the TFT, and at least one upper light shielding film of the laminate body is electrically connected with the TFT and the pixel electrode.
Also, according to the present invention, there is provided a semiconductor device comprising: a substrate; a lower light shielding film located on the substrate; a TFT located over the lower light shielding film; a pixel electrode electrically connected with the TFT; a laminate body which is located between the TFT and the pixel electrode and has a plurality of upper light shielding films and a plurality of insulating films which are alternately laminated; at least one interlayer insulating film formed over the TFT; and a window formed between the pixel electrode and the substrate by removing the interlayer insulating film, the semiconductor device being characterized in that the window is filled with a transparent organic insulating film for leveling, the plurality of laminated light shielding films are formed from a bottom surface of the window to cover and fit the TFT, and a storage capacitor element is formed by the insulating film and the plurality of upper light shielding films which are formed via the insulating film in the laminate body.
Also, according to the present invention, there is provided a semiconductor device comprising: a substrate; a TFT located over the substrate; a pixel electrode electrically connected with the TFT; a laminate body which is located between the TFT and the pixel electrode and has a plurality of upper light shielding films and a plurality of insulating films which are alternately laminated: at least one interlayer insulating film formed over the TFT; a window formed between the pixel electrode and the substrate by removing the interlayer insulating film; and a wiring for electrically connecting the TFT and the pixel electrode, the wiring being one layer of the upper light shielding films which are formed from a bottom surface of the window to cover and fit the TFT, the semiconductor device being characterized in that an area of the window substantially equal to that of a region which is intended to control display in a pixel.
Also, according to the present invention, there is provided a semiconductor device characterized by further comprising a lower light shielding film formed between the substrate and the TFT.
Also, according to the present invention, there is provided a semiconductor device characterized in that a first layer of the upper light shielding layers is in contact with the lower light shielding film at the bottom surface of the window between the pixel electrode and the substrate.
Also, according to the present invention, there is provided a semiconductor device characterized in that the window includes a photoresist film colored with one of R (red), G (green), and B (blue) and a transparent organic insulating film.
Also, according to the present invention, there is provided a method of manufacturing a semiconductor device characterized by comprising: forming a semiconductor layer over an insulating surface; forming a gate insulating film on the semiconductor layer; forming a gate electrode on the gate insulating film; forming a first interlayer insulating film on the gate electrode; forming a second interlayer insulating film on the first interlayer insulating film; forming a first contact hole which reaches the semiconductor layer and forming a wiring for electrically connecting among respective TFTs; forming a third interlayer insulating film to cover the wiring; forming a groove which reaches a substrate between a region through which light is transmitted and a TFT; continuously forming a light shielding film from a region located over the third interlayer insulating film to the groove; forming a second contact hole for connecting a pixel electrode and the wiring; forming a fourth interlayer insulating film on the light shielding film; removing a portion of an insulating film formed in the second contact hole to expose the wiring; and forming the pixel electrode.
According to the present invention, there is provided a method of manufacturing a semiconductor device characterized by comprising: forming a semiconductor layer over an insulating surface; forming a gate insulating film on the semiconductor layer; forming a gate electrode on the gate insulating film; forming a first interlayer insulating film on the gate electrode; forming a second interlayer insulating film on the first interlayer insulating film; forming a first contact hole which reaches the semiconductor layer and forming a wiring for electrically connecting among respective TFTs; forming a third interlayer insulating film to cover the wiring; removing a base insulating film, the gate insulating film, the first interlayer insulating film, and the second interlayer insulating film in a region through which light is transmitted to form a window which reaches a substrate; forming an upper light shielding film on the third interlayer insulating film to cover a TFT; removing a lower light shielding film formed on a bottom surface of the window; forming a second contact hole in the upper light shielding film; forming a fourth interlayer insulating film on the upper light shielding film; filling the window with a transparent insulating film for leveling; forming a fifth interlayer insulating film on the upper light shielding film; removing a portion of an insulating film filled into the second contact hole to expose the wiring; and forming a pixel electrode on the fifth interlayer insulating film.
According to the present invention, there is provided a method of manufacturing a semiconductor device characterized by comprising: forming a semiconductor layer over an insulating surface; forming a gate insulating film on the semiconductor layer; forming a gate electrode on the gate insulating film; forming a first interlayer insulating film on the gate electrode; forming a second interlayer insulating film on the first interlayer insulating film; forming a first contact hole which reaches the semiconductor layer and forming a wiring for electrically connecting among respective TFTs; forming a third interlayer insulating film to cover the wiring; removing a base insulating film, the gate insulating film, the first interlayer insulating film, and the second interlayer insulating film in a region through which light is transmitted to form a hole which reaches a substrate; forming an upper first light shielding film on the third interlayer insulating film to cover a TFT; forming a second contact hole which reaches the wiring in the upper first light shielding film and the third interlayer insulating film; forming a first insulating film on the upper first light shielding film; removing a portion of the first insulating film filled into the second contact hole to expose the wiring; forming an upper second light shielding film on the first insulating film; forming a second insulating film on the upper second light shielding film; forming an upper third light shielding film on the second insulating film; removing a lower light shielding film, the upper first light shielding film, the first insulating film, the upper second light shielding film, the second insulating film, and the upper third light shielding film, which are formed on a bottom surface of the hole; forming a third contact hole which reaches the upper second light shielding film in the upper third light shielding film and the second insulating film; forming a fourth interlayer insulating film; filling the hole with a transparent insulating film for leveling; forming a fifth interlayer insulating film on the upper third light shielding film; removing a portion of an insulating film filled into the third contact hole to expose the upper second light shielding film; and forming a pixel electrode on the fifth interlayer insulating film.
Also, according to the present invention, there is provided a method of manufacturing a semiconductor characterized by comprising forming a lower light shielding film on the insulating surface.
Also, according to the present invention, there is provided a method of manufacturing a semiconductor characterized in that a lower light shielding film, the upper first light shielding film, and the upper third light shielding film are connected with a wiring having a ground potential.
Also, according to the present invention, there is provided a method of manufacturing a semiconductor characterized in that a lower light shielding film is in contact with an upper first light shielding film at the bottom surface of the window.
Also, according to the present invention, there is provided a method of manufacturing a semiconductor characterized in that a leveling step for the window is performed using an organic insulating film.
Also, according to the present invention, there is provided a method of manufacturing a semiconductor characterized in that a leveling step for the window is performed by laminating a photoresist film colored with one of R (red), G (green), and B (blue) and a transparent organic insulating film.
Also, according to the present invention, there is provided a method of manufacturing a semiconductor characterized in that the semiconductor layer is crystallized by irradiation of laser light.
Also, according to the present invention, there is provided a method of manufacturing a semiconductor characterized in that the semiconductor layer is a crystalline semiconductor layer obtained by reducing a concentration of a catalytic element in the semiconductor layer by gettering the catalytic element after crystallization using the catalytic element.
As described above, according to the present invention, the structure is used in which the TFT is covered with the light shielding film to prevent the occurrence of a photo leak current by light incident into the semiconductor layer of the TFT without intention, such as diffracted light or stray light.